(1) Field of the Invention
The present invention relates to a method for computing a real time matched field response using sensor outputs of a passive sonar array.
(2) Description of the Prior Art
Matched field processing (MFP) is a sonar signal processing technique that incorporates acoustic propagation modeling into signal processing algorithms. MFP provides for localization of an acoustic point source in three dimensions.
In operation, the MFP beamformer matches the sound pressure field measured by an array of hydrophone sensors with a replica. The replica is derived from an acoustic propagation model and presumes a specific location for the acoustic source. That is, each hypothetical location of the presumed sound source determines, in conjunction with oceanic acoustic propagation parameters, a particular replica.
Each replica is matched with the measured field, and the maximum values computed by the MFP represent the replicas that most closely represent the received, measured signal. This information enables the MFP to estimate the location of a sound source in range (distance), bearing and depth.
Previous methods for computing a broadband matched field surface have various shortcomings. In a first shortcoming, the methods are computationally expensive. The methods are also not suitable for producing results in real time because the methods do not compute results at a rate equal to the rate of the incoming sensor data. Furthermore, the methods use stationary, vertically oriented arrays and cannot be used on mobile, horizontally towed sensor arrays. Also, no previous method efficiently compensates for the changing shape of a towed array of sensors.
As such, a need exists for computing a broadband matched field surface in real time as an improved method of determining the distance, angular bearing and depth of an acoustic source relative to a sonar sensor array. Preferably, the method would be flexible and mobile as well as comparatively inexpensive to existing methods.